That's not what they're saying. They're saying that you can't steal the creature that the Conscripts fought (say, a Grizzly Bears) if that creature (the Grizzly Bears) dies. Whether or not the Conscripts dies is irrelevant.
1. Since it's not specified, you have to play the spell then and there, during the resolution of the ability. Contrast Mind's Desire, which offers a duration for when you can play the spells ("until end of turn".)
While there is (presumably) a correct cut to take one's deck down to 40 cards, it's not always possible to find that cut, for whatever reason (time constraints, card evaluation skill level, etc.) In such a case, the slight advantage of having one fewer card in the deck is outweighed by the possible negative consequences of cutting the wrong card.
Edit: Also what magicmerl said about mana ratios & stuff.
Does your LGS normally do pool swaps for Sealed events? I've never seen a pool swap occur at a Regular REL event (like a Prerelease). You probably don't need to worry.
Though combat damage is dealt simultaneously, there are three distinct damage events occurring, one for each creature. Your Pridemate will get three +1/+1 counters.
Wait...you don't get to play with the same deck you built out of your sealed pool?
You don't build your deck out of the pool you initially register. You'll get a pool that someone else registered, then build your deck out of that. This is done to prevent cheating.
This works fine. As the turn ends, the original controller of the Soul Seizer will regain control of the Ghastly Haunting - the fact that the creature transformed into an enchantment doesn't change anything. This player will now control the creature that the Haunting enchants.
Kismet doesn't have a triggered ability (note the lack of the words "When", "Whenever", or "At".) It just modifies the way your lands, etc., enter the battlefield. This is redundant with your Guildgate's own ability; it will enter tapped as normal. Then, since the trigger condition for Amulet is met, Amulet will trigger and untap the Guildgate.
I know that paying the Cost of LED is going to pitch that Flayer into his graveyard, can I get some help convincing him thouroughly?
The issue is that LED can be activated only any time you could cast an instant. This means you can't be in the process of casting a spell when you use it: you would have to activate its ability before casting the Flayer if you wanted to use its LED mana, but that would mean that Flayer wouldn't be in your hand by the time you could cast it.
Edit: There's also some threshold guys that are kinda like that, actually. One second.
Here:
Kinda forgot about the entire Odyssey block there
(Though generally I prefer traditional Storm combo decks.)
2. It's your call in both scenarios.
Edit: Also what magicmerl said about mana ratios & stuff.
(nath'd obv)
You don't build your deck out of the pool you initially register. You'll get a pool that someone else registered, then build your deck out of that. This is done to prevent cheating.
Traitorous Blood
Ghastly Haunting
This works fine. As the turn ends, the original controller of the Soul Seizer will regain control of the Ghastly Haunting - the fact that the creature transformed into an enchantment doesn't change anything. This player will now control the creature that the Haunting enchants.